1. Field of the Invention
The present invention relates to a brushless alternator which is mounted, for example, in a vehicle.
2. Description of the Related Art
A brushless alternator including a shaft, a rotor, and a stator is conventionally known (for example, see JP 02-133053 A (FIG. 6)). In the conventional brushless alternator, the shaft is rotatably provided in a case constituted by a pair of brackets through an intermediation of a bearing on a central axis of the case. The rotor is fixed to the shaft, and has N-poles and S-poles formed alternately along a direction of rotation. The stator surrounds the rotor. The rotor includes a field coil and a pair of pole cores. A current is made to flow through the field coil to generate a magnetic flux. Each of the pair of pole cores includes a plurality of claw-like magnetic pole portions and a yoke portion. The pair of pole cores cover the field coil to be respectively magnetized to the N-pole and the S-pole by the magnetic flux.
In the case of the brushless alternator described above, the field coil obtained by winding a conductor around a spool is fixed to one of the brackets through an intermediation of the yoke portion of one of the pole cores. A distal end portion of the spool is fitted into a concave portion of the one of the brackets.
In the conventional brushless alternator, the distal end portion of the spool is simply fitted into the concave portion of the one of the brackets. In addition, the field coil and the yoke portion are fixed to the one of the brackets substantially only by mounting bolts. Therefore, a gap is locally generated between the yoke portion and the bracket due to fine surface roughness of surfaces of the one of the brackets and the yoke portion, which are brought into contact with each other, and a difference in flatness between the surfaces.
With the generation of the gap, water penetrates into the gap from exterior. Subsequently, the water passes through a gap between the distal end portion of the spool and the concave portion of the bracket to reach the bearing. As a result, there is a problem that the bearing is degraded to generate abnormal sounds or the bearing is damaged by the generation of rust.
Moreover, the generation of the gap between the surface of the yoke portion and the surface of the bracket, which are brought into contact with each other, inclines the mounting portions of the yoke portions and the field coil with respect to the bracket to cause a malfunction in a magnetic circuit of the pole cores. Moreover, the spool abuts against the pole cores. Thus, there is another problem that the operation of the rotor is destabilized.